The present invention relates generally to battery operated devices powered by a removable main power source, and provided with an auxiliary power source as a battery backup device, and methods for operating the same. In principle, the auxiliary power device can be any device that can store energy for a predetermined time, such a battery, a large charged capacitor, or the like. Such battery operated devices include communication devices such as pagers, mobile radio handsets, cordless telephones, or the like.
Current battery backed devices deal with the removal of the removable main power source by resetting the device after the main power source is replaced and attempt to restore and/or recover any information which was stored in the device. Any operation which was in progress when the main power source was removed, either physically or as the result of a battery bounce, is aborted. Resetting the device and attempting recovery has caused numerous software defects to be inserted. This is because the device could have been in any state prior to the main power source or battery being removed and therefore the associated variables or data were in a modified state. After resetting the device, every possible variable/data combination needed to be accounted for, otherwise the device would not be reset and powerup correctly. Such current devices also cause the user to become annoyed when, in the middle of a long operation, either a battery bounce or other main power source removal causes the device to reset, thereby forcing the user to duplicate the operation.
Other battery backed devices deal with hardware and/or mechanical mechanisms to replace the main power source with a backup cell when the main power source is removed. These solutions do not elaborate on the operation of the device while the main power source is removed or on the operation when the main power source is replaced. In such solutions, typically the device is reset when the main power source is replaced and extensive validation of the data has to be performed to determine if RAM data need to be cleared. Upon any type of battery bounce these solutions will cause a device reset and attempt to recover memory. This has proven to be unacceptable to users. Some examples are if the user is in the process of setting time or alarms and the device is dropped causing a battery bounce of the main power source. Upon resetting, the alarms/time may be in an unknown state, causing the user to proceed back to the screens and reenter the data. Examples of such hardware and/or mechanical mechanisms are disclosed in the U.S. Pat. No. 5,369,802, where a break-before-make-switching arrangement is provided for guaranteeing that first contact is made with a new battery replacing the old battery which is to be removed, in the British Patent Application GB 2 270 445, where data is stored upon detection of battery removal using a switch, and the Japanese Patent Application 0 07107027 A, where a built-in battery takes over while the main power source is being replaced.
In the European Patent Application EP 0 607 919, a software solution is provided in which the current operating state of the device is stored in a non-volatile RAM upon detection of electrical disconnection of the main power source. Additionally, the current time of the device is stored in the RAM as well. Depending on the applied microprocessor platform storing the operating state in non-volatile RAM has the following disadvantages. Non-volatile RAM must be set aside for the specific purpose of storing the operating state. This would require a considerable amount of storage. Particularly low end, i.e., cheap microprocessor or hardware designs such as applied in pagers, for instance, cannot afford to have this much memory dedicated for this purpose. This considerable amount of RAM is required due to the fact that a significant number of registers will need to be backed up upon detection of a primary battery removal so as to save the operating state. In this solution it is also necessary to know what the operating state is at all times. Since the non-volatile RAM is not part of the core-CPU RAM, it is essential that a checksum be performed on the operating state which has been backed up into non-volatile RAM as the nonvolatile RAM is only valid while the backup cell has enough voltage to maintain the non-volatile RAM. If there is no checking performed on the operating state when it is reloaded then there is substantial risk of an invalid state being reloaded causing unpredictable results. Furthermore, the method does not allow for the time of the device to be updated upon the main power source being replaced. For instance, if the main power source was removed at a given time and was left out for 10 minutes, then upon replacing the main power source, the time would be restored with a ten minutes time difference. A separate clock chip is needed to keep track of the time, which is an additional component requiring power. Low cost products would require a minimum number of components.
Thus, what is needed is a simpler and more reliable method and device for replacement of the main power source or for battery bouncing, or the like, preferably allowing battery replacement to be performed without causing user aggravation to duplicate an operation.